Lens system, interchangeable lens device, and camera system

Abstract

A lens system in the present disclosure includes: a first lens group that is moved toward an image side along an optical axis in focusing from a far-object in-focus state to a near-object in-focus state, and has positive optical power; and a second lens group that is disposed on the image side relative to the first lens group and has optical power. The lens system satisfies the following conditions (1) and (2). 0.5<| fg 1/ WD |<2.0  (1) 20<| fg 2/ f |<700  (2) where fg1 is a focal length of the first lens group, WD is a distance, on the optical axis, from an object surface to a lens surface located closest to an object side of the first lens group, fg2 is a focal length of the second lens group, and f is a focal length of the lens system under the far-object in-focus state.

What is claimed is: 
     
       1. A lens system comprising:
 a first lens group that is moved toward an image side along an optical axis in focusing from a far-object in-focus state to a near-object in-focus state, and has positive optical power; and 
 a second lens group that is disposed on the image side relative to the first lens group and has optical power, 
 
       wherein
 the following conditions (1) and (2) are satisfied:
   0.5<| fg 1/ WD|< 2.0  (1)
 
   20<| fg 2/ f|< 700  (2)
 
 
 where 
 fg1 is a focal length of the first lens group, 
 WD is a distance, on the optical axis, from an object surface to a lens surface located closest to an object side of the first lens group, 
 fg2 is a focal length of the second lens group, and 
 f is a focal length of the lens system under the far-object in-focus state. 
 
     
     
       2. The lens system according to  claim 1 , comprising a cemented lens constituted by three lens elements in the first lens group. 
     
     
       3. The lens system according to  claim 1 , wherein
 a first lens element included in the first lens group and disposed closest to the object side, satisfies the following conditions (3) and (4):
   1.7<ndA<2.5  (3)
 
   13<νdA<45  (4)
 
 
 where 
 ndA is a refractive index of the first lens element at d line, and 
 νdA is an Abbe number of the first lens element at the d line. 
 
     
     
       4. The lens system according to  claim 1 , wherein
 a first lens element disposed closest to the object side of the first lens group has a positive meniscus shape with a convex surface facing the image side, and satisfies the following condition (5):
   1<( R 1 A+R 2 A )/( R 1 A−R 2 A )<15  (5)
 
 
 where 
 R1A is a curvature radius of a surface on the object side of the first lens element, and 
 R2A is a curvature radius of a surface on the image side of the first lens element. 
 
     
     
       5. The lens system according to  claim 1 , wherein
 the second lens group satisfies the following condition (6):
   0.1< t 2 max/tg 2<0.8  (6)
 
 
 where 
 t2max is a maximum value of distances, on the optical axis, between lens elements in the second lens group, and 
 tg2 is a distance, on the optical axis, from a lens surface located closest to the object side of the second lens group, to a lens surface located closest to the image side of the second lens group. 
 
     
     
       6. The lens system according to  claim 1 , wherein
 the focal length of the first lens group, and a focal length of a first lens element included in the first lens group and disposed closest to the object side, satisfy the following condition (7):
   −3< fg 1/ fL<− 1  (7)
 
 
 where 
 fg1 is the focal length of the first lens group, and 
 fL is the focal length of the first lens element. 
 
     
     
       7. An interchangeable lens device comprising:
 the lens system according to  claim 1 ; and
 a lens mount part capable of connecting to a camera body including an image element for receiving an optical image formed by the lens system and converting the optical image into an electric image signal. 
 
 
     
     
       8. A camera system comprising:
 an interchangeable lens device including the lens system according to  claim 1 ; and 
 a camera body that is detachably connected to the interchangeable lens device via a camera mount part and includes an image element for receiving an optical image formed by the lens system and converting the optical image into an electric image signal.